1. Field of the Invention
The present invention relates to an optical disk device, and more particularly to data recording in a ZCLV method in which an optical disk is divided into a plurality of zones in a radial direction and each zone is subjected to CLV (constant linear velocity) control.
2. Description of the Related Art
In optical disk devices, several control methods are employed, such as CLV (constant linear velocity) control, CAV (constant angular velocity) control, and ZCLV control in which an optical disk is divided into a plurality of zones and each zone is controlled at a constant linear velocity which varies among the zones. Although the CLV control method is now the most common employed for recording data on an optical disk because improvement in recording quality is relatively easy to achieve with this method, enhancement in recording speed under the CLV control is hampered by the upper limit of the rate of revolution at the innermost periphery of the disk. More specifically, under the CLV control the revolution speed is highest at the innermost periphery, and the upper limit of the rate of revolution imposed by electric or mechanic restriction at the innermost periphery determines the linear velocity in the CLV method.
According to the ZCLV technique, in order to maximize the recording speed, the linear velocity is varied for each zone, rather than fixed throughout the disk. For example, even though the linear velocity of 16 times faster than the normal velocity (hereinafter referred to as “16×”) is the upper limit for the innermost zone, the linear velocities of 20× and 24× can be obtained at the middle and outer zones, respectively, with the same revolution speed. Therefore, an optical disk is divided into three zones, an inner, middle, and outer zone, for recording data at 16×, 20×, and 24× velocities, respectively.
However, the number of zones and the linear velocities are fixed in the ZCLV control system, and little consideration has been given on optimization of the number of zones and the linear velocity for each zone.
In an example wherein an optical disk is divided into two zones, i.e. inner and outer peripheral zones, and that the upper limit of the rate of revolution at the innermost periphery of the disk is 16×, when the linear velocity of a zone 1 on the inner peripheral side is set at 16×, and that of a zone 2 on the outer peripheral side is set at 32×, the disk position where the 32× linear velocity can be obtained with the rate of revolution of 16× corresponds to approximately 51 minutes. Therefore, when the amount of data to be recorded is smaller than 51 minutes, all data is recorded at 16×. When the amount of data to be recorded is 79 minutes, data for 51 minutes is recorded at 16×, and the remaining data for 28 minutes is recorded at 32×. The time required to record the data is:
recording time at 16×—3 minutes and 11 seconds
recording time at 32×—53 seconds
total—4 minutes and 4 seconds
On the other hand, when the linear velocity of the outer peripheral zone 2 is changed from 32× to 24× for recording the same data of 79 minutes, the disk position where the 24× linear velocity can be obtained with the rate of revolution of 16× corresponds to approximately 21 minutes. Consequently, data for 21 minutes is recorded at 16× while the remaining data for 58 minutes is recorded at 24×. As a result, the time required for recording the data is as follows:
recording time at 16×—1 minute and 19 seconds
recording time at 24×—2 minutes and 25 seconds
total—3 minutes and 44 seconds
Comparing the time periods in these two examples, it can be appreciated that the total recording time is reduced by approximately 20 seconds by changing the linear velocity in the outer peripheral zone from 32× to 24×. Thus, the recording time period varies with the linear velocity for each zone, and with the number of divided zones. The recording time cannot be reduced simply by increasing the linear velocity for each zone, or by increasing the number of divided zones.